Bruce Gunn, the QueenslandBureau of Meteorology state manager, said tropical cyclone Oma could cause significant coastal erosion and water levels could exceed the highest tide of the year.

Modelling from Europe and the U.S. shows the system could hit the Queensland coast by the end of the week, bringing 200km/h winds and up to 500mm of rain to the state's southeast, but meteorologist Kimba Wong said there were still many different scenarios for how the cyclone will develop.

Brisbane was also put on notice, despite the bureau expecting TC Oma, the first cyclone to threaten to strike the city in nearly three decades, to turn northwards at the last minute.

Oma is now about 820km northeast of Brisbane.

Bureau of Meteorology forecaster Adam Blazak said there was still disagreement about which path the storm will take, but there was a possibility it could make landfall at the weekend.

The weather system was already bringing hazardous surf conditions and abnormally high tides.

All beaches on the Sunshine Coast and Gold Coast have been closed, with authorities saying waves could reach eight metres over the weekend.

But it is expected to strengthen back to a Category Two on Friday.

But that doesn't mean the state will be spared its effects, with warnings issued for high winds and unsafe swell coinciding with king tides along the east coast from Thursday.

After that, its behaviour is less predictable.

"We are starting to see the main swell packet from Oma starting to arrive on the south coast of Queensland now", Mr Hall told ABC radio.

"It's looking increasingly likely that it will track close to the southeast Queensland coast, (but) it's hard to say how close it will get at the moment", she said.

Closer to Fiji and New Caledonia than the Australian mainland, Oma is tracking ominously southwest, with a growing number of predictive models forecasting the cyclone will cross the Queensland coast between Mackay and Fraser Island.

'These conditions are then expected to extend south over the remaining southeastern Queensland coast during this evening and Friday.

As daring beach-goers have captured wonderful photos of the unsafe swell, forecasters are warning that ocean conditions will worsen before Cyclone Oma actually hits. The Bureau has issued a flood watch from Gladstone to the New South Wales border.

The storm may linger off the coast only.

While it is unusual for a cyclone to track this far south, it is not unprecedented.